<article id="wikiArticle">
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<h2 id="Summary" name="Summary">概述</h2>
<p><code><strong>Math.expm1()</strong></code> 函数返回 <code>E<sup>x</sup> - 1</code>, 其中 <code>x</code> 是该函数的参数, <code>E</code> 是自然对数的底数 <code>2.718281828459045.</code></p>
<h2 id="Syntax" name="Syntax">语法</h2>
<pre><code class="language-javascript"><code>Math.expm1(<em>x</em>)</code></code></pre>
<h3 id="Parameters" name="Parameters">参数</h3>
<dl>
<dt><code>x</code></dt>
<dd>任意数字.</dd>
</dl>
<h2 id="Description" name="Description">描述</h2>
<p><code><span style="color: #4d4e53; font-family: 'Open Sans',sans-serif; line-height: 21px;">参数 </span><code style="font-size: 14px; line-height: inherit; margin: 0px; padding: 0px; border: 0px; color: rgb(77, 78, 83);">x</code><span style="color: #4d4e53; font-family: 'Open Sans',sans-serif; line-height: 21px;"> 会被自动类型转换成 </span><code style="font-size: 14px; line-height: inherit; margin: 0px; padding: 0px; border: 0px; color: rgb(77, 78, 83);">number </code><span style="color: #4d4e53; font-family: 'Open Sans',sans-serif; line-height: 21px;">类型.</span></code></p>
<p><code>expm1 是 "exponent minus 1" 的缩写.</code></p>
<h2 id="Examples" name="Examples">示例</h2>
<pre><code class="language-js">Math.expm1(1)     // 1.7182818284590453
Math.expm1(-38)   // -1
Math.expm1("-38") // -1
Math.expm1("foo") // NaN
</code></pre>
<h2 id="Polyfill">Polyfill</h2>
<p>因为我们已经有了 <code>Math.exp </code>函数, 所以很容易 polyfill.</p>
<pre><code  class="language-javascript">Math.expm1 = Math.expm1 || function (x) {
    return Math.exp(x) - 1
}
</code></pre>
<h2 id="规范">规范</h2>
<table class="standard-table">
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<th scope="col">Specification</th>
<th scope="col">Status</th>
<th scope="col">Comment</th>
</tr>
<tr>
<td><a class="external" href="https://www.ecma-international.org/ecma-262/6.0/#sec-math.expm1" hreflang="en" lang="en" rel="noopener">ECMAScript 2015 (6th Edition, ECMA-262)<br/><small lang="zh-CN">Math.expm1</small></a></td>
<td><span class="spec-Standard">Standard</span></td>
<td>Initial definition.</td>
</tr>
</tbody>
</table>
<h2 id="浏览器兼容性">浏览器兼容性</h2>
<p></p><div class="blockIndicator warning"><strong><a class="external" href="https://github.com/mdn/browser-compat-data" rel="noopener">We're converting our compatibility data into a machine-readable JSON format</a></strong>.
            This compatibility table still uses the old format,
            because we haven't yet converted the data it contains.
            <strong><a class="new" href="/zh-CN/docs/MDN/Contribute/Structures/Compatibility_tables" rel="nofollow">Find out how you can help!</a></strong></div>
<div class="htab">
<a id="AutoCompatibilityTable" name="AutoCompatibilityTable"></a>
<ul>
<li class="selected"><a>Desktop</a></li>
<li><a>Mobile</a></li>
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<div id="compat-desktop">
<table class="compat-table">
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<th>Feature</th>
<th>Chrome</th>
<th>Firefox (Gecko)</th>
<th>Internet Explorer</th>
<th>Opera</th>
<th>Safari</th>
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<td>Basic support</td>
<td><span style="color: #f00;">未实现</span></td>
<td><a href="/en-US/Firefox/Releases/25" title="Released on 2013-10-29.">25</a> (25)</td>
<td><span style="color: #f00;">未实现</span></td>
<td><span style="color: #f00;">未实现</span></td>
<td><span style="color: #f00;">未实现</span></td>
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<div id="compat-mobile">
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<th>Feature</th>
<th>Android</th>
<th>Chrome for Android</th>
<th>Firefox Mobile (Gecko)</th>
<th>IE Mobile</th>
<th>Opera Mobile</th>
<th>Safari Mobile</th>
</tr>
<tr>
<td>Basic support</td>
<td><span style="color: #f00;">未实现</span></td>
<td><span style="color: #f00;">未实现</span></td>
<td>25.0 (25)</td>
<td><span style="color: #f00;">未实现</span></td>
<td><span style="color: #f00;">未实现</span></td>
<td><span style="color: #f00;">未实现</span></td>
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</table>
</div>
<h2 id="See_also" name="See_also">相关链接</h2>
<ul>
<li><a href="Reference/Global_Objects/Math" title="Math 是一个内置对象， 它具有数学常数和函数的属性和方法。不是一个函数对象。"><code>Math</code></a> 对象.</li>
</ul>
</article>